Charge protection circuit, charger, electronic device, and charge protection method

ABSTRACT

Disclosed is a charge protection circuit including: a switch that switches between allowing and not allowing power supply from an external power source to a charging circuit that supplies power for charging a rechargeable battery; a detector that detects at least one of a current flowing from the charging circuit to the rechargeable battery and a voltage between two electrodes of the rechargeable battery; a determiner that determines whether a detection result of the detector is abnormal; and a controller that, in response to the determiner determining that the detection result of the detector is abnormal, causes the switch to switch to an interrupting state so as to interrupt power supply to the charging circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 16/558,672 filed on Sep. 3, 2019 which is basedupon and claims the benefit of priority under 35 U.S.C. 119 of JapanesePatent Application No. 2018-173251 filed on Sep. 18, 2018 the entiredisclosure of which, including the description, claims, drawings, andabstract, is incorporated herein by reference in its entirety.

BACKGROUND

The technical field relates to a charge protection circuit, a charger,an electronic device, and a charge protection method.

A charger that charges a rechargeable battery has various types ofsafety mechanisms in a charging circuit that prevent abnormal poweroutput to the rechargeable battery in order to prevent troubles such asoverheating due to overcharging of the rechargeable battery and ashort-circuit current and to charge the battery at a stable voltage. Forexample, Japanese Patent Application Publication No. 2001-28838 (JP2001-28838 A) discloses a charger that prevents erroneous charging byinterrupting the voltage supply from an AC adapter when the voltagesupplied from the AC adapter is abnormal.

However, the charger disclosed in JP 2001-28838 A may fail toappropriately respond to an abnormal operation of a charging circuititself.

SUMMARY

One of the aspects is a charge protection circuit including: a switchthat switches between allowing and not allowing power supply from anexternal power source to a charging circuit that supplies power forcharging a rechargeable battery; a detector that detects at least one ofa current flowing from the charging circuit to the rechargeable batteryand a voltage between two electrodes of the rechargeable battery; adeterminer that determines whether a detection result of the detector isabnormal; and a controller that, in response to the determinerdetermining that the detection result of the detector is abnormal,causes the switch to switch to an interrupting state so as to interruptpower supply to the charging circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the functional configuration ofan electronic device;

FIG. 2A illustrates the corresponding relationship between the poweroutput from a charging circuit and the control operation;

FIG. 2B illustrates the corresponding relationship between the poweroutput from the charging circuit and the control operation;

FIG. 3 is a flowchart illustrating the control steps of a chargeabnormality monitoring process;

FIG. 4 is a block diagram illustrating the functional configuration ofan electronic device according to Modification 1; and

FIG. 5 is a block diagram illustrating the functional configuration ofan electronic device according to Modification 2.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, exemplary embodiments will be described with reference tothe accompanying drawings.

FIG. 1 is a block diagram illustrating the functional configuration ofan electronic device 1 according to the present embodiment.

The electronic device 1 includes a charger 10, a power supply adapter20, a rechargeable battery 30, and a functional block 40.

The charger 10 receives power supplied from an external power source,and outputs power to the rechargeable battery 30 to charge therechargeable battery 30.

The power supply adapter 20 converts (A-D converts) the power input froman external power source (commercial AC power source in the presentembodiment) into a predetermined DC voltage, and supplies the DC voltageto the charger 10. The power supply adapter 20 includes, for example, aplug for an outlet of the commercial power source, and automaticallystarts input and output of power when the plug is inserted into theoutlet.

The rechargeable battery 30 supplies power required for operations ofthe functional block 40. The rechargeable battery 30 is a rechargeablebattery, such as a lithium-ion battery, capable of outputting storedpower. The rechargeable battery 30 may be detachable from the charger10, or may be independent from the charger 10 and replaceable.Alternatively, the rechargeable battery 30 may be an integral unit ofthe charger 10.

The functional block 40 implements operations of the electronic device1. The functional block 40 may include, but not specifically limited to,a display and an operation interface, for example. Specifically, thefunctional block 40 may include a liquid crystal display and a touchsensor overlaid thereon so as to perform display operations and detectuser inputs from the outside. The functional block 40 may furtherinclude sensors that measure physical quantities such as temperature,acceleration, and magnetic field, and an output unit that outputs soundand/or vibration. The functional block 40 may be powered by therechargeable battery 30 directly through a cable (not illustrated).

The following describes the charger 10 in more detail.

The charger 10 includes a charging circuit 11, a switching element 12(switch), a current & voltage detection circuit 13 (detector), acontroller 14, a resistive element 15, and a diode 16.

Based on the power input from the external power source through thepower supply adapter 20, the charging circuit 11 outputs a current forcharging the rechargeable battery 30 so as to supply power to be storedin the rechargeable battery 30. The charging circuit 11 canappropriately convert the input DC power (current and voltage), andoutput the converted power. The charging circuit 11 outputs apredetermined current, or a current at the substantially rated voltageof the rechargeable battery 30, to the rechargeable battery 30, based onthe amount of power stored in the rechargeable battery 30. When thevoltage between two electrodes (referred to as a storage voltage) of therechargeable battery 30 is close to the rated voltage, the chargingcircuit 11 outputs a current at the substantially rated voltage. Thus,when the storage voltage becomes equal to the rated voltage, the outputcurrent becomes zero. Further, the charging circuit 11 includes a knownovercharge prevention circuit so as not to charge the rechargeablebattery 30 to a predetermined upper limit or greater. Thus, when thestorage voltage of the rechargeable battery 30 reaches the upper limit,the charging circuit 11 stops the current output. After stopping thecurrent output, the charging circuit 11 does not restart the chargingoperation until the storage voltage falls below a predeterminedreference value, which is lower than the upper limit.

The switching element 12 switches between whether to allow the powersupplied to the charger 10 to be input to the charging circuit 11. Theswitching element 12, which is, for example, an analog switch in thepresent embodiment, can reversibly switch between allowing and notallowing power supply to the charging circuit 11 in accordance with acontrol signal from the controller 14. The switching element 12 is anormally-ON element, and allows power supply when in a basic state suchas when a control signal from the controller 14 is not input, or wheninput of a control signal is started (or restarted).

The current & voltage detection circuit 13 detects an output currentflowing from the charging circuit 11 to the rechargeable battery 30 anda voltage applied to the rechargeable battery 30, that is, the level ofcurrent flowing to the rechargeable battery 30 and the level of voltagebetween two electrodes of the rechargeable battery 30 (which is equal toa voltage applied by the charging circuit 11 to the rechargeable battery30), and outputs signals indicating the detection results to thecontroller 14 (detecting step). The current & voltage detection circuit13 may determine whether the current and the voltage are greater thantheir reference values, and output the detection results in the form ofbinary signals. Alternatively, the current & voltage detection circuit13 may obtain (measure) the current value and the voltage value, andoutput the obtained values themselves to the controller 14. Then, thecontroller 14 may compare these values to their reference values. Thecurrent & voltage detection circuit 13 outputs the detection results atpredetermined monitoring intervals (first detection intervals) of, forexample, 1 to 10 seconds. The voltage detection by the current & voltagedetection circuit 13 may be utilized not only for detecting the charge(power storage) status during charging, but also for detecting theremaining amount of stored power during discharge of the rechargeablebattery 30. The monitoring interval (second detection interval) usedwhen charging is not performed may be longer than the first monitoringinterval used when charging is performed, and may be, for example, 1 to10 minutes in the present embodiment. In this case, the controller 14serves as a second determiner to determine whether power is suppliedfrom the external power source to the charging circuit 11 through thepower supply adapter 20. The controller 14 serves as a detectioninterval setter to set the monitoring interval to 1 to 10 seconds (firstdetection interval) when power is supplied to the charging circuit 11,and set the monitoring interval to 1 to 10 minutes (second detectioninterval) when power is not supplied to the charging circuit 11 (whencharging is not performed). A determination as to whether power issupplied from the power supply adapter 20 to the charging circuit 11 maybe made based on the current input from the input terminal side of thecharging circuit 11 to the controller 14 through the diode 16.Alternatively, a current detection circuit may be separately providedupstream of the charging circuit 11 such that the controller 14 obtainsthe detection result, or a circuit that detects whether power issupplied may be provided in the charging circuit 11 such that thecontroller 14 obtains the detection result.

Further, as will be described below, when the controller 14 detects anabnormality based on the detection result of the current & voltagedetection circuit 13 and switches the switching element 12 to the OFFstate (state in which power supply is interrupted), the monitoringinterval may be set back to 1 to 10 minutes.

The controller 14 determines whether an abnormality is detected based onthe detection result of the current & voltage detection circuit 13(serves as a determiner), and controls switching of the switchingelement 12 between the two states (that is, switching between allowingand not allowing power supply) in accordance with the detection result.As described above, the controller 14 can switch the switching element12 to either the ON state (state in which power supply is allowed) orthe OFF state (state in which power supply is interrupted). When thedetection result indicates that the current or voltage is equal to orgreater than its reference value, the controller 14 determines that anabnormality is detected and switches the switching element 12 to the OFFstate to interrupt power supply. Whereas, when both the current andvoltage are less than their reference values, the controller 14 switchesthe switching element 12 to the ON state. The controller 14, whichincludes a central processing unit (CPU) and a random access memory(RAM), operates with power supplied from the power supply adapter 20 orthe rechargeable battery 30 through the diode 16. Further, thecontroller 14 outputs a control signal to the functional block 40 of theelectronic device 1 to control the operations. Even when the functionalblock 40 of the electronic device 1 is not operating, the controller 14may become continuously or intermittently active so as to continuouslycharge and monitor the rechargeable battery 30. Alternatively, acontroller that controls operations of the functional block 40 may beprovided separately from the controller 14.

Among the elements described above, at least the switching element 12,the current & voltage detection circuit 13, and the controller 14 form acharge protection circuit 10 a of the charger 10.

The following describes how the controller 14 controls the switchingoperation of the switching element 12.

FIGS. 2A and 2B illustrate the corresponding relationship between thepower output from the charging circuit 11 and the control operation.Note that the changes in current and voltage, in particular, therelationship between their rising rate and falling rate illustrated inFIGS. 2A an 2B are merely an example, and do not necessarily representactual values.

For example, the charging circuit 11 outputs the charging power at aconstant current when the stored voltage of the rechargeable battery 30is low, and at a substantially constant voltage after the storagevoltage becomes equal to or greater than a predetermined voltage. In thecharging at the substantially constant voltage, the current graduallydecreases as the storage voltage approaches the constant voltage, andeventually the charging current becomes substantially zero when thecharging ends.

As illustrated in FIG. 2A, in the case where a storage voltage V issufficiently lower than an upper limit VU, when the internal voltageexceeds the original set voltage or a short circuit occurs due to anabnormality of the charging circuit 11 while outputting power forcharging, an output current Ic increases (timing t1). Then, the risingrate of the storage voltage V becomes continuously high, and the currentexceeding the upper limit IU is detected at the timing of monitoring bythe current & voltage detection circuit 13 (timing t2). Upon detectingthe output current greater than the upper limit IU (reference currentvalue), the controller 14 switches a control signal S of the switchingelement 12 from ON to OFF. Then, the switching element 12 interruptspower supply, so that power is not supplied to the charging circuit 11.Accordingly, the output current Ic from the charging circuit 11 becomeszero.

As illustrated in FIG. 2B, in the case where the storage voltage V ishigh, when the output current Ic of the charging circuit 11 increases(timing t1), the storage voltage V quickly reaches the upper limit VU.Thus, the overcharge prevention circuit of the charging circuit 11operates to turn OFF the control signal S, so that the current output isstopped. After the output current Ic becomes “0”, the storage voltage Vgradually decreases due to consumption of power by the controller 14 andother elements. When the storage voltage V falls below the referencevalue VL, the current output is restarted. However, the storage voltageV quickly rises again due to the abnormality, so that the current outputis stopped. That is, the output current Ic exhibits pulsed fluctuationsat short intervals, and the storage voltage V of the rechargeablebattery 30 exhibits sawtooth fluctuations at the same intervals.

As described above, the current & voltage detection circuit 13 obtainsand outputs the detection results at predetermined monitoring intervals.Therefore, if the output pulse width of the output current Ic is small,it may take time until an abnormal current is detected due to the lackof coincidence with the timing of monitoring. In the present embodiment,since a monitoring reference value VF (reference voltage) is lower thanthe upper limit VU and the reference value VL of the overchargeprevention circuit (but higher than a set voltage for normal charging atthe substantially constant voltage), the storage voltage V remains abovethe monitoring reference value VF when the output of the chargingcircuit 11 is abnormal. Thus, the abnormality is reliably detected. Upondetecting a voltage greater than the monitoring reference value VF, thecontroller 14 switches the switching element 12 to interrupt powersupply (timing t2).

In the charge protection circuit 10 a, the controller 14 causes theswitching element 12 to switch between allowing and not allowing powersupply. Therefore, after power supply from the power supply adapter 20is interrupted, power supply from the rechargeable battery 30 to thecontroller 14 needs to be maintained for a sufficient time period.Therefore, when causing the switching element 12 to interrupt powersupply, the controller 14 restricts operations other than operations forcontrolling switching of the switching element 12, that is, theoperations of the functional block 40, thereby reducing the powerconsumption by the functional block 40. For example, as for the displayof the functional block 40 that provides a visual notification of anabnormality of the charger 10 (charging circuit 11), the controller 14may set an upper limit for the luminance of the visual notification.Further, the controller 14 may prevent activation of applicationprograms other the control programs for the basic operations of thecontroller 14, and prompt the user to end the running applicationprogram. Meanwhile, the controller 14 does not have to restrict some ofthe operations of the functional block 40, for example, operationsperformed as the operation interface, that is, detection of user inputsand output of detection signals to the controller 14.

FIG. 3 is a flowchart illustrating the control steps of a chargeabnormality monitoring process executed by the controller 14 in thecharger 10. The charge abnormality monitoring process is started insynchronization with the monitoring intervals in the current & voltagedetection circuit 13.

When a charge abnormality monitoring process is started, the controller14 obtains the output current Ic and the storage voltage V from thecurrent & voltage detection circuit 13 (step S101). The controller 14determines whether the output current Ic is greater than the upper limitIU (step S102). If the output current Ic is greater than the upper limitIU (“YES” in step S102), the process of the controller 14 proceeds tostep S104.

If the output current Ic is not greater than (equal to or less than) theupper limit IU (“NO” in step S102), the controller 14 determines whetherthe storage voltage V is greater than the monitoring reference value VF(step S103). If the output current Ic is greater (“YES” in step S103),the process of the controller 14 proceeds to step S104.

When the storage voltage V is not greater than (equal to or less than)the monitoring reference value VF (“NO” in step S103), the controller 14outputs an ON signal to the switching element 12 to allow power supply(step S105). Then, the controller 14 ends the charge abnormalitymonitoring process.

When the process proceeds from step S102 or S103 to step S104, thecontroller 14 outputs an OFF signal to the switching element 12 tointerrupt power supply (step S104). Then, the controller 14 ends thecharge abnormality monitoring process.

Among these steps, the steps S102 and S103 correspond to the operationsperformed as the determiner of the present embodiment (determiningstep), and the step S104 corresponds to the operation performed as acontroller of the present embodiment (switching step).

FIG. 4 is a block diagram illustrating the functional configuration ofan electronic device 1 according to Modification 1.

In this electronic device 1, the charger 10 includes a fuse 12 a and aswitching element 12 b as a switch in place of the switching element 12.The fuse 12 a is disposed between the power supply adapter 20 and thecharging circuit 11, and is cut when a current equal to or greater thana predetermined current value flows through it. The switching element 12b is located between the fuse 12 a and the charging circuit 11, andbetween the fuse 12 a and ground. The switching element 12 b turns ON inresponse to a signal input from the controller 14, and forms ashort-circuit path that passes through the fuse 12 a from the powersupply adapter 20.

Upon detecting an abnormality from the detection results of the current& voltage detection circuit 13, the controller 14 turns ON the switchingelement 12 b. Thus, a short-circuit current that flows through ashort-circuit path cuts the fuse 12 a, so that power supply to thecharging circuit 11 is interrupted. That is, once the charge protectioncircuit 10 a interrupts power supply, the charge protection circuit 10 amaintains the interrupting state. In this case, the charging circuit 11and the fuse 12 a may be replaced, or the entire charger 10 may bereplaced, depending on cost and labor involved. Alternatively, theentire electronic device 1 may be replaced.

FIG. 5 is a block diagram illustrating the functional configuration ofan electronic device 1 according to Modification 2.

This electronic device 1 is provided with a latching switch 12 c, inplace of the switching element 12 serving as the switch of the aboveembodiment. The method of latching is not specifically limited. Uponreceiving, from the controller 14, a control signal for switching to theOFF state (interruption of power supply from the power supply adapter20), the latching switch 12 c switches to the OFF state and mechanicallylatches (maintains) the OFF state. The OFF state is canceled in responseto a reset signal from the controller 14, or through a manual operationby the user. That is, even when the controller 14 determines that thedetection result of the current & voltage detection circuit 13 is nolonger abnormal, or even when the controller 14 stops operating and asignal from the controller 14 is lost, the latching switch 12 c remainsOFF and power supply is not restarted. However, the latching switch 12 citself is not broken. Therefore, the latching switch 12 c may be usefulwhen the failed charging circuit 11 in the charger 10 is replaceable.

As described above, the charge protection circuit 10 a of the charger 10provided in the electronic device 1 according to the present embodimentincludes: the switching element 12 that switches between allowing andnot allowing power supply from the external power source to the chargingcircuit 11 that supplies power for charging the rechargeable battery 30;the current & voltage detection circuit 13 that detects at least one ofthe current flowing from the charging circuit 11 to the rechargeablebattery 30 and the voltage between two electrodes of the rechargeablebattery 30; and the controller 14 that determines, as the determiner,whether the detection result of the current & voltage detection circuit13 is abnormal, and causes, as the controller, the switching element 12to interrupt power supply to the charging circuit 11 when the detectionresult is abnormal.

With this configuration, when the output of the charging circuit 11becomes abnormal, the abnormality is detected, so that power supply tothe charging circuit 11 is interrupted. Therefore, it is possible to notonly prevent overcharging of the rechargeable battery 30, but alsoquickly detect the abnormality of the charging circuit 11 itself andstop its operation. Accordingly, it is possible to reduce troubles dueto overheating of the components such as the charger 10 and therechargeable battery 30.

Further, the switching element 12 allows power supply when in a basicstate. Therefore, at initial startup or every time the electronic device1 and the charger 10 are started, normal charging and power supply canbe quickly started without performing initial setup of the switchingelement 12.

Further, the controller 14 controls operations of the electronic device1 provided with the charge protection circuit 10 a. When the electronicdevice 1 is being started, the switching element 12 is in the basicstate in which power supply is allowed. That is, normally, when theelectronic device 1 is being started, power can be supplied from eitherthe rechargeable battery 30 or the power supply adapter 20, and it ispossible to freely switch between the two, based on the usage by theuser. Therefore, as long as no abnormality occurs in the charger 10, theelectronic device 1 can be used with no limitations, without especiallymaking settings.

Further, with the provision of a pair of the fuse 12 a and the switchingelement 12 b of Modification 1, or with the provision of the latchingswitch 12 c of Modification 2, the charge protection circuit 10 a may beconfigured to, once it switches to an interrupting state in which powersupply is interrupted, maintain the interrupting state. In this manner,it is possible to prevent power from being supplied again to thecharging circuit 11 without making any repair after interruption ofpower supply.

Further, the charge protection circuit 10 a of Modification 1 includesthe fuse 12 a, and interrupts power supply by cutting the fuse 12 a.Thus, by physically disconnecting the fuse 12 a, it is possible to morereliably interrupt power supply to the charging circuit 11. Especially,in the case of replacing the entire charger 10 or the entire electronicdevice 1 to eliminate the abnormality instead of making repairs, powersupply is completely interrupted with the simple configuration describedabove. Therefore, it is possible to reliably prevent the chargingcircuit 11 from receiving power again and generating heat although notneeded.

Further, in the charge protection circuit 10 a of Modification 2, thelatching switch 12 c is used that is configured to, once it switches tothe interrupting state in which power supply is interrupted, maintainthe interrupting state. Thus, after power supply is interrupted, thelatch that maintains the interrupting state can be reset. Therefore, itis possible to prevent power from being supplied before the chargingcircuit 11 is repaired or replaced, and use the charger 10 again afterthe serviceman makes repairs and reset the latch.

Further, the controller 14 causes the switching element 12 to switchbetween allowing and not allowing power supply in accordance withwhether the detection result is abnormal. Thus, switching of theswitching element 12 may be performed based simply on the current state.Thus, as soon as the charging circuit 11 is restored, power supply canbe quickly restarted. Meanwhile, even if the charging circuit 11 remainsabnormal, the switching element 12 immediately interrupts power supplyagain. Therefore, no problem occurs.

Further, the controller 14 controls operations of the electronic device1 provided with the charge protection circuit 10 a, and restricts atleast one of operations other than switching control of the switchingelement 12 when causing the switching element 12 to interrupt powersupply. After power supply from the external power source isinterrupted, the electronic device 1 operates with the power remainingin the rechargeable battery 30. Accordingly, by restricting otheroperations, it is possible to make the controller 14, which controlsoperations of the switching element 12, operate for a longer time.

Further, the current & voltage detection circuit 13 detects the currentflowing to the rechargeable battery 30, and the controller 14 causes theswitching element 12 to interrupt power supply when the current detectedby the current & voltage detection circuit 13 is greater than the upperlimit IU of the current. Thus, by quickly interrupting power supplybased on the current flowing to the rechargeable battery 30, it ispossible to prevent heat generation due to a large current and toprevent overcharging and resultant troubles.

Further, the current & voltage detection circuit 13 detects a voltagebetween two electrodes of the rechargeable battery 30, and thecontroller 14 causes the switching element 12 to interrupt power supplywhen the voltage detected by the current & voltage detection circuit 13is greater than the monitoring reference value VF.

If a large current flows due to a short circuit, a protection circuitmay immediately operate to interrupt the current output. However, inthis case, if current detection is performed at relatively longmonitoring intervals, the large current might not be detected. Thus, bydetecting the level of voltage that is lower than the voltage detectedas an overvoltage and that is reached when a current output responsiveto a large current is interrupted, occurrence of the large current canbe detected through an excess voltage even while the large current isinterrupted. Therefore, it is possible to more reliably respond to anabnormality of the charging circuit 11 and to interrupt power supply tothe charging circuit 11.

Further, the controller 14 determines, as the second determiner, whetherpower is supplied from the external power source to the charging circuit11, and variably sets, as the detection interval setter, a detectioninterval at which the current & voltage detection circuit 13 detects atleast one of the current flowing from the charging circuit 11 to therechargeable battery 30 and the voltage between two electrodes of therechargeable battery 30.

The current & voltage detection circuit 13 may be used for not onlydetection of a charge abnormality, but also detection of the amount(remaining amount) of power stored in the rechargeable battery 30. Byusing the same element for different purposes, it is possible to preventan increase in size and cost. In this case, appropriate monitoringintervals may be determined based on the differences in changes incurrent and voltage between charging and discharging. Thus, it ispossible to prevent unneeded operations, and an increase in powerconsumption.

Further, the controller 14 sets, as the detection interval setter, thedetection interval to a first detection interval when power isdetermined to be supplied from the external power source to the chargingcircuit 11, and sets the detection interval to a second detectioninterval longer than the first detection interval when power isdetermined not to be supplied from the external power source to thecharging circuit 11. Unlike detection of a charge abnormality, since thevoltage and current during normal consumption of power supplied from therechargeable battery 30 do not change rapidly, detection duringconsumption of power (discharging) may be performed at monitoringintervals (first detection intervals) that are longer than monitoringintervals (second detection intervals) for detection of a chargeabnormality. Accordingly, it is possible to effectively detect currentand voltage at a required frequency in accordance with the purpose.

Further, the controller 14 sets, as the detection interval setter, thedetection interval to the second detection interval when power supply tothe charging circuit 11 is interrupted by the switching element 12. Thatis, in the case where charging is stopped due to a charge abnormality,the situation is treated in the same manner as during normal powerconsumption. Moreover, since the rechargeable battery 30 may need tolast as long as possible without being recharged, power consumption canbe reduced by changing the settings as described above to increase themonitoring interval.

Further, the charger 10 of the present embodiment includes: the chargeprotection circuit 10 a; and the charging circuit 11 that receives powersupplied from the external power source, and charges the rechargeablebattery 30. In this configuration, the charge protection circuit 10 areliably detects an abnormality of the charging circuit 11 andinterrupts power supply to the charging circuit 11. Therefore, it ispossible to charge the rechargeable battery 30 more safely and promptly.

Further, the electronic device 1 of the present embodiment includes thecharger 10 described above. Thus, it is possible to more reliably reducetroubles such as overheating of the electronic device 1, and operate theelectronic device 1 using the rechargeable battery 30 safely.

Further, a charge protection method according to the present embodimentincludes: a detecting step of detecting at least one of a currentflowing from the charging circuit 11 to the rechargeable battery 30 anda voltage between two electrodes of the rechargeable battery 30, thecharging circuit 11 supplying power for charging the rechargeablebattery 30; a determining step of determining whether a detection resultin the detecting step is abnormal; and a switching step of interruptingpower supply to the charging circuit 11 when the detection result isdetermined to be abnormal. With this method, input to the chargingcircuit 11 is interrupted in response to an abnormal output of thecharging circuit 11. Thus, it is possible to more reliably reducetroubles of the charger 10 and the rechargeable battery 30 due to theabnormality of the charging circuit 11.

The present invention is not limited to the embodiment described above,and various modifications may be made.

For example, in the above embodiment, both the output current from thecharging circuit 11 to the rechargeable battery 30 and the appliedvoltage (storage voltage) to the rechargeable battery 30 are detected.However, it is not necessary to detect both the output current and theapplied voltage. The current & voltage detection circuit 13 may beconfigured to detect only the current. In this case, the monitoringinterval of the current may be shorter than that of the aboveembodiment. Alternatively, an analog circuit may be used to detect themaximum value in a period, and the detection result based on the maximumvalue may be output to the controller 14 at predetermined monitoringintervals. Further alternatively, only the voltage may be detectedwithout directly detecting the current. In this case, the rising rate ofthe voltage may be taken into account.

Further, in the above embodiment, the switching element 12 is anormally-ON element. However, the switching element 12 may be anormally-OFF element, and switched ON under the control of thecontroller 14. In this case, although the controller 14 is started whenpower is supplied from the rechargeable battery 30 in the aboveembodiment, a circuit that can directly supply power from the powersupply adapter 20 to the controller 14 may be provided.

Further, in the above embodiment, the monitoring reference value VF(reference voltage) is lower than the upper limit VU and the referencevalue VL of the overcharge prevention circuit (but is higher than theset voltage for normal charging at the substantially constant voltage).However, the monitoring reference value VF may be set to between theupper limit VU and the reference value VL. In this case, no abnormalityis detected in the period from when the storage voltage falls below themonitoring reference value VF to when the storage voltage falls to thereference voltage VL and a large current flows again. Therefore, thesevalues may be appropriately determined relatively to each other based onthe monitoring interval and other factors so as to prevent anunnecessary delay in detection of an abnormality.

In the above embodiment, the controller 14 is implemented as software bythe CPU. However, the present invention is not limited thereto. Thecontroller 14 may be implemented as a hardware circuit that compares thevoltage and the current to the monitoring reference value VF and theupper limit IU, respectively, and outputs signals based on thecomparison results to the switching element 12.

The charge protection circuit 10 a may be an independent circuit thatcan be externally attached to the charger 10.

The charger 10 does not have to be provided in the electronic device 1,and may be an independent charger.

Further, the specific details, such as the elements, and the arrangementand control operations of the elements, described in the aboveembodiments may be modified within the scope of the present invention.

Although some embodiments have been described, the present invention isnot limited to the above embodiments, and the scope of the presentinvention is defined by the appended claims and their equivalents.

What is claimed is:
 1. A charge protection circuit comprising: a switchthat switches between allowing and not allowing power supply from anexternal power source to a charging circuit that supplies power forcharging a rechargeable battery; a detector that detects a chargedvoltage V between two electrodes of the rechargeable battery; a firstdeterminer that determines whether the charged voltage V detected by thedetector is higher than a monitoring reference value VF; and acontroller that, in response to the first determiner determining thatthe charged voltage V detected by the detector is greater than themonitoring reference value VF, causes the switch to switch to aninterrupting state so as to interrupt the power supply to the chargingcircuit, wherein the charging circuit includes an overcharge preventioncircuit that prevents the rechargeable battery from being charged over apredetermined upper limit VU, and wherein the monitoring reference valueVF is lower than the upper limit VU, lower than a reference value VL forresuming a current output from the charging circuit when the chargedvoltage V falls below the reference value VL, and higher than a setvoltage for normal substantially constant-voltage charging.
 2. Thecharge protection circuit according to claim 1, wherein in response tothe charged voltage V reaching the upper limit VU, the controlleroperates the overcharge prevention circuit to stop the current output,and wherein in response to the charged voltage V falling below thereference value VL, the controller resumes the current output.
 3. Thecharge protection circuit according to claim 1, wherein the switchallows the power supply when in a basic state.
 4. The charge protectioncircuit according to claim 3, wherein the controller controls operationsof an electronic device provided with the charge protection circuit, andthe basic state includes a state at the time when the electronic deviceis started.
 5. The charge protection circuit according to claim 1,wherein once the switch switches to the interrupting state in which thepower supply is interrupted, the switch maintains the interruptingstate.
 6. The charge protection circuit according to claim 5, whereinthe switch includes a fuse and interrupts the power supply by cuttingthe fuse.
 7. The charge protection circuit according to claim 6, whereinthe switch includes a latching switch that maintains the interruptingstate once the switch switches to the interrupting state in which thepower supply is interrupted.
 8. The charge protection circuit accordingto claim 1, wherein the controller causes the switch to switch betweenallowing and not allowing the power supply in accordance with whetherthe detection result is abnormal.
 9. The charge protection circuitaccording to claim 3, wherein the controller causes the switch to switchbetween allowing and not allowing the power supply in accordance withwhether the detection result is abnormal.
 10. The charge protectioncircuit according to claim 4, wherein the controller causes the switchto switch between allowing and not allowing power the supply inaccordance with whether the detection result is abnormal.
 11. The chargeprotection circuit according to claim 8, wherein the controller controlsoperations of an electronic device provided with the charge protectioncircuit, and restricts at least one of operations other than switchingcontrol of the switch when causing the switch to interrupt the powersupply.
 12. The charge protection circuit according to claim 1, whereinthe detector detects the current flowing from the charging circuit tothe rechargeable battery; the first determiner determines that thedetection result of the detector is abnormal when the current detectedby the detector is greater than a reference current value; and inresponse to the first determiner determining that the detection resultof the detector is abnormal, the controller causes the switch to switchto the interrupting state so as to interrupt the power supply.
 13. Thecharge protection circuit according to claim 1, further comprising: asecond determiner that determines whether power is supplied from theexternal power source to the charging circuit; and a detection intervalsetter that, based on a determination result of the second determiner,variably sets a detection interval at which the detector detects atleast one of the current output from the charging circuit to therechargeable battery and the charged voltage V between the twoelectrodes of the rechargeable battery, wherein the detection intervalsetter variably sets the detection interval in response to the seconddeterminer determining that power is supplied from the external powersource to the charging circuit, and sets the detection interval to aconstant value in response to the second determiner determining that thepower is not supplied from the external power source to the chargingcircuit.
 14. The charge protection circuit according to claim 13,wherein the detection interval setter sets the detection interval to afirst detection interval in response to the second determinerdetermining that power is supplied from the external power source to thecharging circuit, and sets the detection interval to a second detectioninterval longer than the first detection interval in response to thesecond determiner determining that power is not supplied from theexternal power source to the charging circuit.
 15. The charge protectioncircuit according to claim 14, wherein the detection interval settersets the detection interval to the second detection interval in responseto power supply to the charging circuit being interrupted by the switch.16. A charger comprising: the charge protection circuit of claim 1; anda charging circuit that receives power from an external power source andcharges a rechargeable battery.
 17. An electronic device comprising: thecharger of claim
 16. 18. A charge protection method comprising: adetecting step of detecting a charged voltage V between two electrodesof the rechargeable battery; a first determining step of determiningwhether the charged voltage V detected in the detecting step is higherthan a monitoring reference value VF; and a switching step ofinterrupting power supply to a charging circuit for supplying power tocharge the rechargeable battery in response to a determination in thefirst determining step that the charged voltage V detected in thedetecting step is higher than the monitoring reference value VF in thefirst determining step, wherein the charging circuit includes anovercharge prevention circuit that prevents the rechargeable batteryfrom being charged over a predetermined upper limit VU, and wherein themonitoring reference value VF is lower than the upper limit VU, lowerthan a reference value VL for resuming a current output from thecharging circuit when the charged voltage V falls below the referencevalue VL, and higher than a set voltage for normal substantiallyconstant-voltage charging.